In the past, in a compressor of this type, as shown in FIGS. 1 and 2, a stator 104 of a motor 103 for driving a compression mechanism 102 is fixed to the inside of a closed container 101; a crank shaft 106 for driving the compression mechanism 102 is connected with a rotor 105 of the motor 103; and a lubricant oil sump 107 is formed in the lower portion of the closed container 101. The compression mechanism 102 comprises a stationary swirl vane member 110 integrally composed of a stationary frame body 108 and stationary swirl vanes 109, a revolving swirl blade member 113 integrally composed of revolving swirl blades 111 for defining a plurality of compression work rooms 114 as meshing with the stationary swirl vanes 109 and a revolving end plate 112 mounting thereon the revolving swirl blades 111, and a rotation preventing member 115 preventing the rotation of the revolving swirl blade member 113 on its own axis, but only allowing a revolving motion of the same. The revolving end plate 112 is formed at the side opposite to the revolving swirl blades 111 with a revolving motion drive shaft 116, which is fitted in an eccentric bearing 118 eccentrically disposed inside of a main shaft 117 which is formed at one end of the crank shaft 106. This crank shaft 106 is supported by a main bearing member 120, which accommodates a main bearing 119 supporting the main shaft 117, and by an upper bearing member 122, which mounts a plain bearing 121 supporting the crank shaft 106 at the end position thereof opposite to the main shaft. A thrust bearing 123 fixed to the above-mentioned main bearing member 120 supports the revolving end plate 112 in the axial direction. The refrigerant gas suctioned through the suction tube 124 of the compressor flows from an inlet port 125 of the compression mechanism 102 to the compression mechanism, compressed in a compression work room 114, and discharged from an outlet port 126 through a discharge room 127 and an outlet tube 128 to the outside of the compressor. (JP-A-1-177482).
In the above mentioned compressor of a prior art, since the crank shaft 106 holding the rotor 105 is supported at the both ends thereof, the main shaft 117 receives substantially no bending moment, and the bending moment acting on the crank shaft 106 is also small, thereby enhancing the reliability of the compressor. However, the rotary shaft portion of the crank shaft 106 is apt to suffer a galling force in assembling processes, which may generate a vibration of the compressor or a damage of the bearing. Further, the lubrication for the upper bearing 121 is apt to become insufficient, thereby possibly causing damage of a bearing when a plain bearing is used. FIG. 2 shows a solution for the above-mentioned problem. In this drawing, the end portion of the crank shaft 201 opposite to the main shaft 202 is supported by an upper rolling bearing 203. A rolling bearing has an advantage, in comparison with a plain bearing, of being able to bear a radial load and an axial load at the same time, and requiring little lubricant oil for lubrication of the bearing. As a result, the precision in assembling and the control of the oil lubrication is not required to be so strict. (JP-A-1-170779, JP-A-58-172485, JP-A-62-253982). A rolling bearing has, however, a severe problem of generating vibration and noise caused by axial vibration and resonance of the bearing.